Antilocking system (ABS) and propulsion control system (ASR) for a road vehicle.
The invention relates to an antilocking system (ABS) and a propulsion control system (ASR) for a road vehicle with a hydraulic multi-circuit brake system, in which the brakes of the driven vehicle wheels form a static brake circuit connected to an outlet pressure space of a brake unit actuable by a pedal. The ABS antilocking system works on the principle of controlling brake pressure reduction and brake pressure build-up phases of the antilocking control by respectively increasing and decreasing the volume of an ABS control space connected to the wheel brakes. The propulsion ASR control works on the principle of decelerating a vehicle wheel tending to spin by activating its wheel brake until its drive slip remains within a range of values compatible both with good propulsion acceleration and good driving stability.
The invention provides for an activatable brake pressure regulating valve for controlling pressure reduction, pressure build-up and pressure holding phases of both the antilocking ABS control and the propulsion ASR control, which is movable out of a through flow position relating to the pressure reduction and pressure build-up phases of the antilocking ABS control and to normal braking not subjected to antilocking control, into a blocking position, related to brake pressure holding phases on the respective wheel brake.
A hydraulic cylinder with a displaceable piston is used for a pressure build-up and pressure reduction regulating of the antilocking ABS control A drive pressure space alternatively connectable by the activatable brake pressure regulating valve to an outlet Pressure of an auxiliary pressure source and to a pressureless tank is used to move the piston. The piston valve is displaceable between end positions by pressure in the drive pressure space to define with the hydraulic cylinder, minimum and maximum volumes of an ABS control space which, during normal braking and in pressure reduction and pressure build-up phases of the antilocking ABS control, is connected by the activatable brake pressure regulating valve with at least one of the wheel brake or brakes of the static brake circuit.
The hydraulic cylinder has an ASR outlet pressure space as a pressure build-up and pressure reduction regulating means of the propulsion ASR control and which is connectable by the activatable brake pressure regulating valve to the outlet pressure space of the brake unit and to the brake circuit of the driven vehicle wheels. The ASR outlet space has a variable area defined by the hydraulic cylinder and piston displaceable in the direction of a brake pressure build-up when the drive pressure space is connected to the outlet pressure of the auxiliary pressure source and to a pressure reduction when the drive pressure space is connected to a non-pressure source.
ABS and ASR function control valves are provided, which in sequence, connect the drive pressure space with the non-pressure source and with the pressure outlet of the auxiliary pressure source for providing pressure reduction and pressure build-up at the wheel brakes for respective control phases of the antilocking ABS and propulsion ASR control.
Such a combination of an antilocking system and of a propulsion control system is the subject of the applicant's own older patent application P 37 06 662.5 not previously published.
In the subject of this older patent application, each wheel brake, which can be subjected to the antilocking control, has assigned to it a hydraulic cylinder which acts as a buffer accumulator. The accumulator space is connected to the wheel brake and at the same time forms a portion of the brake line branch leading to the particular wheel brake. The space is defined in a pressure-type manner by the cylinder piston forming a control pressure space which, under valve control, can be connected to the high-pressure outlet of an auxiliary pressure source or alternatively to its pressureless tank or can be shut off from both. Inserted between the brake pressure outlet, assigned to the respective brake circuit, of the brake unit and the accumulator space of the hydraulic cylinder assigned to the respective wheel brake is an electrically activatable pressure inlet control valve, the basic position of which is the open position. In the open position, brake pressure can be fed into the connected wheel brake, in normal braking, that is to say braking not subject to an antilocking control, as a result of actuation of the brake unit or, as with activation of the propulsion ASR control on a driven vehicle wheel, as a result of valve controlled connection of the pressure outlet of an auxiliary pressure source to the brake circuit of the driven vehicle wheels During starting of the vehicle, and/or after the end of a braking operation, and/or at regular time intervals during motoring, the control pressure spaces of the buffer accumulators are connected briefly, via function control valves assigned individually to the hydraulic cylinders, to the pressure outlet of the auxiliary pressure source provided for propulsion ASR control, after which the function control valves are once again switched back from this excited connecting position into their basic position, namely a blocking position.
As a result, as long as the antilocking ABS control does not respond, the pistons of the hydraulic cylinders are maintained in their end positions linked to a minimum volume of the accumulator spaces and are locked hydraulically in these end positions. To obtain a pressure reduction phase on a wheel brake subjected to the antilocking ABS control, pressure inlet control valves are moved into a blocking position and the control pressure space of the buffer accumulator assigned to the appropriate wheel brake is connected to the pressureless tank of the auxiliary pressure source by changing over its function control valve to its pressure reduction position. This results in the piston of the buffer accumulator moving with the effect of increasing the accumulator space connected to the wheel brake and the desired pressure drop is thus obtained due to the increased space. By switching the function control valve back into its basic neutral blocking position, the brake pressure can subsequently be maintained at a lowered value appropriate for control purposes. A brake pressure rebuild up phase of the antilocking ABS control, necessary at a later stage, can be obtained if the control pressure space of the hydraulic cylinder is Connected to the high-pressure outlet of the auxiliary pressure source by Changing over the associated function control valve to its pressure build-up position. This results in the piston of the hydraulic cylinder again experiencing a displacement with the effect of decreasing the volume of its accumulator space and the brake fluid previously discharged into this accumulate space is forced back into the wheel brake once more. This requires that the outlet pressure level of the auxiliary pressure source is higher than the highest possible brake pressure which can be built up in the wheel brakes as a result of the actuation of the brake unit.
Within the framework of the propulsion ASR control device, connected to the brake circuit of the driven vehicle wheels is a further hydraulic cylinder which acts as a pressure reducer. An ASR function control valve connects this cylinder to the high-pressure outlet of the auxiliary pressure source or its tank, or is shut off from both. As a result, brake pressure build-up, brake pressure reduction and brake pressure holding phases of the propulsion ASR control can be selected, the latter also as a result of the alternate or joint shut off of the inlet control valves used both for the antilocking ABS and for the propulsion ASR control.
The brake unit is shut off from the brake circuits of the vehicle for the duration of a propulsion ASR control cycle.
Regardless of favorable properties of the control devices according to the older patent application P 37 06 662.5, which are to be seen especially in that, during normal braking, the pistons of the hydraulic cylinders provided for the antilocking control and for the propulsion control do not have to be displaced, and therefore their position seals cause no frictional losses, although this would be a disadvantage if, in the event of a failure of the brake booster, braking had to be carried out by pedal force alone. This control system combination is also afflicted with some disadvantages:
Since, when the antilocking control responds, the buffer accumulator of the wheel brake subjected to the control is shut off from the brake unit as a result of the closing of the pressure inlet control valve, the driver obtains a reaction, detectable on the brake pedal, to the response of the ABS antilocking control only when the control has responded on all the wheel brakes combined in the brake circuit, and even then only in the form of an arresting of the brake pedal. However, this brake pedal reaction is unfavorable in as much as it can be misunderstood by the driver. For example, the driver may take this to mean that the brake system has failed completely, which in many cases will lead to a panic reaction from the driver.
Even if restoring springs, which force the buffer accumulator pistons into their basic positions linked to a minimum volume of the accumulator spaces, are made weak, problems occur. Even if the minimum pre-stress and the maximum pre-stress of these springs are equivalent to a pressure of only a few bars, this still has the unfavorable consequence, when the antilocking ABS control responds at low absolute values of the brake pressure, in that the residual pressure which is caused by the pre-stress of the restoring springs and below which the brake pressure cannot be lowered by a pressure reduction phase of the antilocking control, corresponds to a still appreciable proportion of the brake pressure, previously fed into the wheel brakes Therefore, under unfavorable circumstances, the control does not result in a sufficient lowering of the brake pressure.
In addition, the construction of the combined antilocking ABS and propulsion ASR control system according to the older patent application also involves a considerable technical outlay. Although the two buffer accumulators of the dual brake circuit are combined in constructional terms to form a compact constructional unit, nevertheless integration of the pressure converter required for the propulsion control into this hydraulic unit, owing to the necessary insertion of the inlet control valves between the pressure converter and the buffer accumulators, is scarcely feasible in technical terms because it involves an extremely high outlay in terms of construction.
It is true that, in relation to a vehicle with all-wheel drive, German Offenlegungsschrift No. 3 531 137 makes known a combined antilocking ABS and propulsion ASR control system which does not have the disadvantages mentioned above as regards the response of the antilocking ABS control at low brake pressures and no, or at least unclear, notification of the response of the antilocking ABS control. In this combined antilocking ABS and propulsion ASR control system, there are pressure modulators which are assigned individually to the wheel brakes. Each performs the function of a single circuit master cylinder for the drive which there is a double acting hydraulic cylinder having, in addition to a drive pressure space into which the outlet pressure of the pedal actuable brake circuit is fed during normal braking, but also a counter pressure space. As a result of a valve controlled connection of the counter pressure space to an auxiliary pressure source, the piston of the pressure modulator is displaceable, counter to the effect of the drive pressure in the direction of a pressure reduction in the outlet pressure space of the modulator connected to the particular wheel brake. Propulsion ASR control phases can be controlled by coupling the auxiliary pressure source to the drive pressure space of the pressure modulator and shutting off the latter from the outlet pressure space of the brake unit of the brake system.
However, the known antilocking ABS and propulsion ASR control system therein, as compared with the subject of the older patent application, is afflicted with a series of major disadvantages:
Because of the large number of axially successive functional spaces of the pressure modulators, a very large constructional length is required.
The multiplicity of piston seals necessary for sealing off the various functional spaces from one another causes high frictional losses, the result of which can be that, in the event of a failure of the brake booster, the brake system required disproportionately high actuating forces, so that even this malfunction can deceive the driver into thinking that the entire brake system has failed. Because of the numerous piston seals of the pressure modulators, the pistons of which are displaced even during normal braking, the susceptibility to wear of the brake system as a whole is also increased.
Starting from a propulsion control device, combined with an antilocking ABS system of the type mentioned in the introduction, the object of this invention is to improve such a control system in such a way that, while ensuring a simple design and a low susceptibility to faults of the control system, a more sensitive response of the antilocking ABS control at low brake pressures and a reliable notification of the response of the antilocking ABS control are achieved. Also, a space saving constructional integration of the hydraulic antilocking ABS and propulsion ASR control regulating elements becomes possible in a simple way.
The invention provides that a hydraulic cylinder and piston include at least one hydraulic step cylinder with a regulating piston having two piston flanges of differing diameters. One piston flange cooperates with the step cylinder to define the ASR outlet pressure space, and the other piston flange cooperates with the step cylinder to define the ABS control space.
A movable drive piston moves the regulating piston to decease in volume the ASR outlet pressure space and build up the brake pressure in at least one wheel brake, or alternatively, to increase in volume the ABS control space and reduce the brake pressure in at least one wheel brake. The regulating piston is coupled via a piston rod passing displaceably in a pressure tight manner through an intermediate wall of the cylinder housing to the drive piston. The drive piston with the hydraulic cylinder movably defines the drive pressure space which is connected to output pressure of an auxiliary pressure source to build up the pressure therein and to a non-pressure source to relieve the pressure therein.
The drive piston is responsive to increased pressure in the drive Pressure space to move the regulating piston in a direction to increase the ABS control space and decrease the ASR outlet-pressure space and, in response to the release of pressure in the drive pressure space, to move the regulating piston in a direction to decrease the ABS control space and increase the ASR outlet-pressure space. The drive piston is biased by a restoring spring into its basic position corresponding to the minimum volume of the ABS control space.
Accordingly, a brake circuit subjected both to the propulsion ASR control and to the antilocking ABS control utilizes at least one hydraulic cylinder designed as a step cylinder and having a working piston with two piston flanges of differing diameters. One piston flange forms the movable wall of an ASR outlet pressure space, as a result of the decrease in volume of which, brake pressure can be built up in the connected wheel brakes. The other piston flange forms a movable wall of an ABS control space, as a result of the increase in volume of which, brake pressure can be reduced in the connected wheel brakes. This working piston is coupled in terms of movement, via a piston rod passing displaceably in a pressure tight manner through an intermediate wall of the cylinder housing, to a drive piston movably defining a wall of the drive pressure space. As result of valve controlled pressure subjection and relief, the drive piston and the coupled working piston are displaceable, respectively, in the direction of an increase of the ABS control space and a decrease of the ASR outlet pressure space, or a decrease of the ABS control space and an increase of the ASR outlet pressure space. The composite piston structure comprising the working piston and the drive piston is biased by a restoring spring into its basic position corresponding to a minimum volume of the ABS control space and maximum volume of the ASR outlet pressure space. There is a control valve arrangement which performs the following functions:
(a) in normal braking, i.e., braking not subject to the antilocking ABS control, both the outlet pressure space of the brake unit and the ASR outlet pressure space and ABS control space are connected to the wheel brakes;
(b) in braking subjected to the antilocking ABS control, only the ABS control space is connected to the brake line (or brake lines) of the controllable brake circuit, and the ASR outlet pressure space is connected to the outlet pressure space of the brake unit;
(c) when the propulsion ASR control responds, the outlet pressure space of the brake unit is shut off from the wheel brakes, the ABS control space is connected to the pressureless brake fluid storage tank of the brake system, and the ASR outlet pressure space is connected to the brake line or lines leading to the wheel brakes.
The antilocking and propulsion control system according to the invention has at least the following advantages:
Since the composite piston structure of a hydraulic cylinder is displaced in the same direction both when the antilocking control responds and when the propulsion control responds, the drive control of this hydraulic cylinder becomes particularly simple. The constructional design of the hydraulic cylinder provided for controlling the antilocking ABS and propulsion ASR control functions likewise becomes correspondingly simple, since it requires only a single drive pressure space. Since the brake pressure reduction and brake pressure build-up phases of the respective control, which initiate an antilocking ABS or propulsion ASR controlled cycle are controlled by subjecting the drive pressure space of the hydraulic cylinder pressure to a pressure space, a rapid response of the particular control is also guaranteed under all circumstances, with the obvious precondition that the hydraulic drive circuit of the hydraulic cylinder be made sufficiently powerful.
By having the drive pressure space is defined by an intermediate wall and by the drive piston in the hydraulic cylinder, the ASR outlet pressure space is defined by the larger piston step of the regulating piston and the intermediate wall.
While the ABS control space is defined by the smaller piston step of the regulating piston and an end wall of the cylinder housing, the ASR outlet pressure space can thus utilize the smaller diameter piston flange, wherein the ABS control space is defined by the larger diameter piston flange. A piston rod couples the drive piston with the regulating piston and passes through a central bore in the intermediate wall, while the drive pressure space is defined by another end wall of the cylinder housing and the drive piston.
This hydraulic cylinder-piston defining system for the ABS and ASR control spaces, as well as the drive pressure space, has the advantage that the spaces defining relative to the housing by the fixed intermediate wall, and the movable drive piston can be utilized for separating the conventionally different pressure mediums of the drive circuit and the control circuit connected hydraulically to the wheel brakes. This is most beneficial in allowing for a short design of the hydraulic cylinder.
By having the drive piston and the regulating piston as separate piston elements, with the regulating piston supported axially on the drive piston by a rod-shaped extension of the piston guided displaceably in a pressure tight manner through a central bore in the intermediate wall of the cylinder housing and with a restoring spring engaging the regulating piston for biasing the regulating piston and the drive piston into a basic position has the advantage in terms of production, that the housing bore receiving the drive piston and those bore steps of the hydraulic cylinder housing, in which the piston flanges of the working piston are guided displaceably in a pressure tight manner, do not have to be centered exactly. This would be necessary if the drive piston were made in one piece with the working piston.
By having the effective amount of a flange surface of the larger flange of the regulating piston defining the ABS control space, and an effective area of flange surface of the smaller flange of the regulating piston, defining the ASR outlet pressure space approximately of equal size within a range of variation of .+-.-15%, ensures that, in control phases the antilocking control, the quantity of brake fluid conveyed back into the outlet pressure space of the brake unit corresponds approximately to that which flows back into the ABS control space from the wheel brakes. This prevents the possibility that the outlet pressure space of the brake unit will be controlled empty and ensures that the driver receives an appropriate notification of the activation of the antilocking control.
In the non-activated state of the control system, the ASR and ABS function control valves provide a hydraulic series connection between the outlet pressure space of the brake unit, the ASR outlet pressure space of the hydraulic cylinder, the ABS control space and at least one brake line leading on to the wheel brakes, and which is actuable mechanically by displacement of the regulating piston of the hydraulic cylinder.
This allows the mechanically actuable control valve to open a central valve located in the regulating piston of the hydraulic cylinder, where the central valve can be maintained in its open position non-activated state of the control system, until the regulating piston has been displaced a small initial portion of its functional stroke, whereupon the central valve assumes its closed position, and wherein there is a control valve which, when the respective control (ABS or ASR) is initiated, is changed from a through flow position providing the series connection between the ASR outlet pressure space and the ABS control space to a position blocking the connection between the ASR outlet pressure space and the ABS control space, a simple circuit is provided.
This constructively particularly simple location of the central valve also provides economies.
It goes without saying that, instead of a central valve integrated in the piston of the hydraulic cylinder, it would also be possible to provide a laterally arranged valve which is accommodated in the housing of the hydraulic cylinder and designed as a seat valve. Here the valve body would be biased by a valve spring into the blocking position of the valve and maintained in its open position by a stop arm interacting with the piston of the hydraulic cylinder, in the basic position of the hydraulic cylinder piston. As a result of such a lateral arrangement of a mechanically actuable valve, constructional length can be saved once again.
The above noted control valve arrangement provided within the antilocking and propulsion control provides various design alternatives which can be produced by simple electrically and/or mechanically and/or hydraulically activated directional valves.
One alternative would have the function control valve comprise a control valve which can be moved out of a basic position, which is assigned to normal braking and to the antilocking ABS control mode in which it connects the outlet pressure space of the brake unit to the ASR outlet pressure space of the hydraulic cylinder, into an excited through flow position, in which the ASR outlet pressure space of the hydraulic cylinder is connected to at least one wheel brake via the brake pressure regulating valve or regulating valves 87 and the outlet pressure space of the brake unit shut off from the ASR outlet pressure space. There, a second function control valve would be movable from a basic position, which corresponds to normal braking and to the antilocking control mode and in which the ABS control space is connected to the wheel brakes of the brake circuit, via a brake pressure regulating valve, to an excited position provided for the ASR control mode and in which the ABS control space is connected with a brake fluid storage tank of the brake system and shut off from the brake circuit. Here, these two function control valves would be 3/2-way solenoid valves receiving output signals from an electronic control unit of the control system for movement into the basic or excited positions necessary for the particular control mode.
Alternatively, one could have the pedal operate on a brake piston to produce a brake pressure in the outlet pressure space with the function control valve comprising two mechanically displaceable controlled valves which, after a small fraction of a brake pressure build-up stroke of the brake piston which reduces the outlet pressure space of the brake unit be moved out of their basic positions into their excited functional positions. Here, one of these two valves would be designed as a 2/2-way valve which in its basic position blocks a flow path leading from the outlet of the ASR outlet pressure space of the hydraulic cylinder to the outlet pressure space of the brake unit and in its excited position opens the flow path. The other of the two mechanically displaceable controlled valves would be designed as 3/2-way valve, which in its basic position provides communication of the ABS control space with the brake circuit, and in its excited position blocks that communication and provides communication between the ABS control space and a brake fluid storage tank. A third 2/2-way solenoid control valve, which in its basic position shuts off a connection of the ASR outlet pressure space from the main brake line of the brake circuit would be moved to an excited position by an ASR function control signal, wherein the ASR outlet pressure space of the hydraulic cylinder is connected to the main brake line portion leading to the at least one wheel brake.
As a variant of this latter system, the function control valve comprises a 3/2-way displacement control valve which, after a small fraction of a pressure build-up stroke of the brake piston reducing the outlet pressure space of the brake unit, would be moved out of its basic position, in which it connects the ABS control space of the hydraulic cylinder to a brake fluid storage tank of the brake system and shuts off the ABS control space from the brake circuit of the vehicle wheels into its excited position in which the ABS control space is connected to brake circuit and is shut off from the brake fluid storage tank. Here, an electrically actuated 3/2-way solenoid control valve which, by an output signal coming from the electronic control unit of the control system in its propulsion ASR control mode would be moved out of its basic normal braking or braking subjected to the antilocking control position in which the outlet pressure space of the brake unit and the ASR outlet pressure space of the hydraulic cylinder would be connected to one another, into its excited position, in which only the ASR outlet pressure space of the hydraulic cylinder is connected to the brake circuit of the controllable vehicle wheels and the outlet pressure space of the brake unit would be shut off from this brake circuit.
In either of these latter two systems, a one-way valve could be inserted between the ASR outlet pressure space of the hydraulic cylinder and the main brake line of the brake circuit in parallel with the third solenoid control valve wherein the one-way valve can open as a result of a higher pressure in the main brake line than in the ASR outlet pressure space of the hydraulic cylinder to permit flow from the main brake line into the ASR outlet pressure space to provide over pressure protection.
A still further alternative would be to have the function control valve comprises a 3/2-way displacement control valve which, after a small fraction of a pressure build-up stroke of the brake piston reducing the outlet pressure space of the brake unit, be moved out of its basic position, in which it connects the ABS control space of the hydraulic cylinder to the brake fluid storage tank of the brake system and shuts off the ABS control space from the brake circuit of the vehicle wheels, into its excited position in which the ABS control space is connected o the brake line of the controllable brake circuit and is shut off from the brake fluid storage tank. Here, a first 2/2-way solenoid control valve would be moved out of its basic normal braking or braking subjected to the antilocking ABS control position by the control system in the propulsion control mode, wherein it connects the outlet pressure space of the brake unit to the ASR outlet pressure space of the hydraulic cylinder into its excited position braking this connection.
Also provided would be a second 2/2-way solenoid control valve which is moved out of its basic normal braking or propulsion ASR control position by a control signal linked to an activation of the control system in its antilocking control mode where it connects the ASR outlet pressure space of the hydraulic cylinder directly to the brake line of the brake circuit to a blocking position closing off the connection.
Another embodiment would have the function control valve comprise two jointly hydraulically activatable valves which, in their basic normal braking and braking subject to the antilocking ABS control position, connect the outlet pressure space of the brake unit with the ASR outlet pressure space of the hydraulic cylinder and also connect the ABS control space of the hydraulic cylinder with the brake circuit of the vehicle wheels, The two function control valves would be movable to their excited propulsion ASR control mode position by the outlet pressure of the auxiliary pressure source, wherein the ASR outlet pressure space would be connected to the brake circuit and the the ABS control space of the hydraulic cylinder is connected to a brake fluid storage tank. In this arrangement, an electrically activatable function control valve would be movable by the control system into its excited propulsion control position, in which a control pressure would be fed into the control spaces of the two hydraulically activatable valves to move them from their basic position to their excited positions, and a relief flow path for relieving the control pressure spaces of the two hydraulically controlled valves which is either open in the basic position of these two valves, or which can be opened at least temporarily by a further control valve would be provided.
Another alternative would have a 2/2-way solenoid control valve which is moved out of its basic propulsion ASR control position by the control system, in which the outlet pressure space of the brake unit is connected to the ASR outlet pressure space of the hydraulic cylinder, into its excited position where it blocks that connection. Here, two hydraulically activatable control valves would be set in basic normal braking and braking subjected to the antilocking ABS control positions when they are connected to a pressureless hydraulic actuation source and to their excited position when connected to a pressure hydraulic source for ASR propulsion control mode. One of the two hydraulically controlled valves would be designed as a 3/2-way valve which, in its basic position connects the ABS control space of the hydraulic cylinder to the brake circuit and in its excited position connects the ABS control space to a pressureless brake fluid storage tank, while the other of the valves would be designed as a 2/2-way valve which, in its basic position blocks the connection of the ASR outlet pressure space of the hydraulic cylinder from the brake circuit and in its excited position connects the ASR outlet pressure space to the brake circuit. Here too, a displacement controlled 2/2-way valve which, after a small fraction of the brake pressure build-up stroke of the brake piston reducing the outlet pressure space of the brake unit would move out of its basic position, connecting the two hydraulic controlled valves to the pressure actuation source at the drive pressure space of the hydraulic cylinder, into an excited position in which the hydraulic valves are disconnected from the drive pressure space and are connected to the pressureless source. This system also lends itself to having a one-way valve inserted between a common control connection of the two hydraulically activatable valves and the drive pressure space of the hydraulic cylinder which is open as a result of a relatively higher actuation pressure for the two hydraulic valves than the pressure in the drive pressure space of the hydraulic cylinder to relieve the actuation pressure if it becomes too large.
Still yet another arrangement is possible wherein the pedal operates a brake piston to produce a brake pressure in the outlet pressure space, in that the function control valve can comprise three mechanically displaceably controlled valves which, after a small fraction of a brake pressure build-up stroke of the brake piston reducing the outlet pressure space of the brake unit, move from their basic non-actuated state of the brake system or propulsion ASR control mode positions into an excited normal braking or braking subjected to the antilocking ABS control positions, and wherein the particular control mode is selected by connecting the drive pressure space of the hydraulic cylinder to the high pressure outlet of the auxiliary pressure source. Under such a system, a first of the mechanically displaceable valves would be a 2/2-way valve which, in its basic position, blocks a flow from an inlet line to an outlet line for connecting the outlet pressure space of the brake unit with the main brake line of the brake circuit and with the ASR outlet pressure space of the hydraulic cylinder where the valve is moved to its active position when the brake system is actuated to open the connection between the pressure space and both the main brake line and the ASR outlet pressure space. A second of the mechanically displaceable controlled 2/2-way valve would be provided which, in its basic position, connects outlet line leading from the first mechanically displaceable valve to the main brake line branching off to the wheel brakes, and in its excited position closing off the outlet line to the main brake line, and a third mechanically displaceable controlled 3/2-way valve would, in its basic Position connects the ABS control space of the hydraulic cylinder to a brake fluid storage tank and in its excited brake system actuated position connects the ABS control space to the main brake line of the brake circuit.
Another alternative would have three mechanically displaceable controlled valves in a basic non-actuated state of the brake system Position, connect the ASR outlet pressure space of the hydraulic cylinder to the main brake line of the controllable brake circuit and disconnect the ABS control space from the main brake line and connect it to a brake fluid storage tank of the brake system. These valves would be movable to an excited position to connect the ABS control space to the main brake line and closes off the connection to the brake fluid storage tank as well as the connection between the ASR outlet pressure space and the ABS control space. Here, an electrically activatable function control valve, actuated by a control signal in response to the activation of the propulsion ASR control would move from a basic position, in which the outlet pressure space of the brake unit is connected to the ASR outlet pressure space of the hydraulic cylinder to an excited blocking position closing this connection.
The three mechanically displaceable controlled valves would comprise 2/2-way change over valves with the first of these connecting the ASR outlet pressure space of the hydraulic cylinder to the main brake line of the static brake circuit, when in its basic position. The second, in its basic position, would block a connection of the ABS control space to the main brake line, while the third, when in its basic position, would connect the ABS control space to a brake fluid storage tank.
Here, a 3/2-way valve would be movable from a basic position connecting the ABS control space to the brake fluid storage tank into an excited position when the brake unit is actuated to close the connection of the ABS control space to the storage tank, and would instead connect the ABS control space to the main brake line of the static brake circuit.
Further designs of control valve arrangements which are alternative to those mentioned above and which make it possible to produce the antilocking and propulsion control system according to the invention by especially simply designed hydraulic cylinders as brake pressure regulating members are possible.
A first of these would comprise a displacement controlled valve which, in a basic non-actuated state of the brake system position, connect the ABS control space of the hydraulic cylinder to a pressure relief means and closes off an initial line leading from the outlet pressure space of the brake unit to the main brake line of the static brake circuit via a further line which also connects with the ASR outlet pressure space of the hydraulic cylinder and which, in an excited brake actuated position connects the ABS control space of the hydraulic cylinder to the main brake line of the brake circuit while also connecting the outlet pressure space of the brake unit to the ASR outlet pressure space of the hydraulic cylinder through the initial and further lines. Here, a first activatable function control valve actuated by the control during normal braking to its basic position connecting the outlet pressure space of the brake unit to the main brake line would be moved by the control into its excited position for the duration of both an antilocking ABS cycle and a propulsion ASR control cycle wherein the connection between the outlet pressure space and the main brake line is closed. A second activatable function control valve would be actuated by the control means into its basic position in which it blocks a flow path leading from the ASR outlet pressure space of the hydraulic cylinder to the main brake line and which, by an output signal linked to the activation of the propulsion ASR control, is moved into its excited position in which the ASR outlet pressure space is connected to the main brake line of the static brake circuit. The first activatable function control valve would be designed as a hydraulically activatable 2/2-way valve which is activated into its blocking position by the outlet pressure of the auxiliary pressure source via a drive/control valve which makes a connection between the drive pressure space of the hydraulic cylinder and the auxiliary pressure source with the hydraulically activatable valve.
A second embodiment would comprise a displacement controlled valve arrangement which, in the basic non-actuated state of the brake system position, connects the ABS control space of the hydraulic cylinder to a pressureless source while also blocking an initial line connecting the outlet pressure space to the brake unit of the main brake line of the static brake circuit through an outlet line and a further valve element of the mechanically actuable valve. Here, the ASR outlet pressure space of the hydraulic cylinder would be likewise connected via this further valve element to the main brake line. Also, the pedal operating a brake piston to produce a brake pressure in the outlet pressure space when the brake system would be actuated, so that, after a small fraction of the pressure build-up stroke of the brake piston reduces the outlet pressure space of the brake unit, the brake piston would move the displacement control valve to its excited position to connect the ABS control space to the main brake line branching off to the wheel brakes of the main brake circuit as well as to shut off the inlet line of the main brake line starting from the outlet pressure space of the brake unit from the outlet line and to shut off the connection of the ASR outlet pressure space of the hydraulic cylinder from the main brake line. Also provided would be a change over valve which, in its basic through flow position connects the ASR outlet pressure space of the hydraulic cylinder to its ABS control space and when it is moved into its excited blocking position disconnecting the ASR outlet pressure space from ABS control space by the control when and for as long as the antilocking ABS or propulsion ASR control is activated.
Preferably, the change over valves would be designed as 2/2-way solenoid valves which are moved into blocking position by an electrical signal appearing for the duration of activation of the control system, or as a hydraulically controlled valve which is moved into its blocking position when and as long as the auxiliary pressure source is coupled to an activation drive pressure space of the valve via the drive/control valve. Here also, there would be a change over valve which, in its basic through flow position connects the outlet pressure space of the brake unit to the main brake line of the static brake circuit and which would be moved into its excited position, for blocking this connection by the control system when and for as long as the control system is activated.
A position indicator which responds to the position of the piston limiting the outlet pressure space of the brake unit and which, in a simplest case, can be designed as a limit switch provides, in a simple way, a safeguard for the system during brake pressure reduction phases of the antilocking control. It is used to prevent too much brake fluid from flowing back into the brake unit and finally into the brake fluid storage tank, as a result of which, when it is necessary for the propulsion control to respond immediately after an antilocking control cycle, its functioning capacity could be impaired. Here, the position indicator would generate an output signal causing the auxiliary pressure source to be disconnected from the drive pressure space of the hydraulic cylinder when, during the course of an antilocking ABS control phase, the piston of the brake unit reaches its basic position or a position immediately adjacent to this.
Having the control valve arrangement comprise two 2/2-way solenoid control valves, one of which in its basic position shuts off the pressure outlet of the auxiliary pressure source from the drive pressure space of the hydraulic cylinder and in its excited position connects this pressure outlet to the auxiliary pressure source, while the other valve, in its basic position connects the drive pressure of the hydraulic cylinder to a pressureless tank of the auxiliary pressure source and in its excited position closes off this connection to the pressureless tank, provides that, in the event of a leak of the valve provided for connecting the drive pressure space of the hydraulic cylinder to the auxiliary pressure source, there cannot be an undesirable pressure build-up in the drive pressure space of the hydraulic cylinder, since pressure medium can flow off to the storage tank of the auxiliary pressure source via the through flow path of the other valve intended for relieving the drive pressure space of the hydraulic cylinder.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.